Anticholinesterase activity of analogs of natural (-)-physostigmine, was measured. (-)-N-Methylphysostigmine was found to be much more potent, whereas unnatural (+)-physostigmine was about 125 times less potent. Fragmentation of (-)-physostigmine in refluxing hexanol afforded (-)-eseroline quantitatively. X-ray diffraction analysis showed rubreserine to contain equal parts of o-quinone and its zwitterion.